This application seeks support for a five-year study of visual perceptual skills in individuals who have severe intellectual disabilities. The goal is to determine the extent to which difficulties in perception affect discrimination learning. Work accomplished during the previous grant period has resulted in an effective, integrated set of methods for assessing and teaching same/different judgements with difficult-to-teach populations. Stimuli used thus far have been forms which differed along several dimensions. In the current project, we ask whether participants are capable of discriminating stimuli that are more similar to one another (i.e., that differ along fewer dimensions). The ability to make such discriminations is essential if participants are to respond differentially to abstract stimuli such as printed letters (e.g., m versus n) or numbers. (e.g., 3 versus 8). To make thee relatively fine discriminations, the defining stimulus differences must be detected (perceived). Until recently, however, the methodological foundation for profiling the perceptual abilities of individuals with severe disabilities did not exist. Our work has established this potential and led directly to the current proposal. In overview, our plan for the next five years is to elaborate and extend procedures we have developed in order to conduct the first truly comprehension of visual perception in individuals with severe retardation and limited language skills.